ui: Remove use of bitmaps when painting tab backgrounds.

ui/gfx/scoped_canvas.h

Index: ui/gfx/scoped_canvas.h
diff --git a/ui/gfx/scoped_canvas.h b/ui/gfx/scoped_canvas.h
index 96ccaffa25d3a28c1f6d4b0295b5224afeeed224..aa2d9830f447989d6f81c9c7ed9ce5d3a0048d0c 100644
--- a/ui/gfx/scoped_canvas.h
+++ b/ui/gfx/scoped_canvas.h
@@ -23,6 +23,17 @@ class GFX_EXPORT ScopedCanvas {
       canvas_->Restore();
   }
 
+  ScopedCanvas(ScopedCanvas&& o) {
+    canvas_ = o.canvas_;
+    o.canvas_ = nullptr;
+  }
+  ScopedCanvas& operator=(ScopedCanvas&& o) {
+    if (canvas_)
+      canvas_->Restore();
+    canvas_ = o.canvas_;
+    o.canvas_ = nullptr;

[danakj, 2017/04/05 22:01:37]

Oops, was missing the return here when I changed these from =default at the last
minute. I realized that would lead to 2 restore for 1 save. The code currently
only uses the constructor (to emplace into optional).

[danakj, 2017/04/05 22:07:01]

Alternatively i could keep passing a null instead of using optional, optional
just seemed more obvious when reading it, lmk.

+  }
+
  private:
   gfx::Canvas* canvas_;